After more than a month of construction delays, the Sinclair finally opened its doors Wednesday in Harvard Square with a performance by ’80s alt-rockers Concrete Blonde. It was good news for the music venue and restaurant after a Tumblr site, The Sinclair Is Not Open, went live earlier this week poking fun at the club’s growing pains. On a private tour of the space earlier Wednesday, it was startling to see how much work remained just a few hours before showtime. The venue’s sign hadn’t been installed yet. Technicians were testing lights, putting black tape on the stage, and awaiting the headliner’s load-in. The bar area was covered with boxes of booze, the ticket booth had computers covered in plastic, and workers were mopping the floors in the restaurant, which chef Michael Schlow will oversee. Josh Bhatti of Bowery Presents: Boston, which will run the venue, seemed relieved by the progress. “Not to downplay people’s frustration,” he said, “but our own frustration with this has been tenfold. It wasn’t pleasant, but we’re glad this is finally happening.”